Imagine the emotions that will be running through him while his loved ones watch while at ease on the parade ground, with his company, he shall be handed a small Marine emblem to attach to his top (field hat is a top in Marine talk). Perhaps his eyes will get a bit wet. A Semper Fi in advance for this recruit, he will soon become a United States Marine.
Not meaning to be an ass, but a Marine's hat is referred to as a cover.